Modern aftertreatment methods for the exhaust gases of diesel engines require the addition of additives to the exhaust gas to allow the respective chemical reactions to take place with optimal effect. Thus, to improve and maintain selective catalytic reduction in the so-called SCR method, ammonia, usually in the form of an aqueous urea solution, must be added to the exhaust gas in a downstream SCR catalyst. Hydrocarbons are added to the exhaust gases to improve and maintain the catalytic function of a diesel oxidation catalyst. Hydrocarbons are also added to the exhaust gases to initiate regeneration of a loaded diesel soot particulate filter.
In many of the aforementioned cases, the additives are injected into the exhaust gas stream in an extremely finely divided form. Then a so-called mixing zone follows downstream from the nozzle, where the exhaust gases and the additives are to be mixed as homogeneously as possible. When using an aqueous urea solution as the additive in particular, this mixing zone must be long enough so that sufficient time remains for the water to evaporate completely.
In addition, it is necessary to ensure that the additives do not come in contact with the pipe wall until it is completely evaporated. Since the pipe wall is usually colder than the exhaust gas itself, the additive would be deposited there. This might result in attack on the pipe but in particular then the proper amount of additive would be missing from the exhaust gas aftertreatment reaction, which would then only take place incompletely. This is unsatisfactory.
The technical world has of course attempted to remedy these disadvantages. In particular it has been proposed that static mixing elements in the form of blades set at a fixed angle, plates and the like should be installed in the mixing zone to achieve a thorough mixing of the two even with a short mixing zone by creating turbulence in the mixture of exhaust gas and additive. Unfortunately, these known proposed approaches have entailed high costs and especially high backpressures. Therefore, there continues to be a substantial demand for technical approaches which will eliminate the disadvantages of the prior art.